A power conversion apparatus has a power conversion function of converting DC power supplied from a DC power supply into AC power to be supplied to an AC electric load such as a rotating electric machine or converting AC power generated by the rotating electric machine into DC power to be supplied to the DC power supply. To fulfill this power conversion function, the power conversion apparatus includes an inverter circuit having a switching device. The switching device repeats a conduction operation and an interruption operation to perform power conversion from DC power to AC power or from AC power to DC power.
For power control for power conversion, a voltage value on a DC power supply side needs to be detected, and a function of measuring the voltage value is generally incorporated in the power conversion apparatus. Meanwhile, commands for power control are calculated by a low-voltage control circuit insulated from a high-voltage target for control.
In a conventional high DC voltage detection method, voltage dividers are connected in series in a multistage manner to convert voltage into one that can be measured in the low-voltage control circuit. In a case in which a resistance value changes due to deterioration or the like of a resistor caused by surges, divided voltage also changes, and accurate measurement cannot be performed. In a case in which accurate high DC voltage detection cannot be performed, this may cause motor control to be unstable and may cause failures of a power module and a capacitor module. Thus, a function of diagnosing abnormalities of the voltage divider is preferably provided.
As an abnormality diagnosis method for a high DC voltage detection circuit, a technique of calculating an estimated fluctuation value of a DC voltage value from a current measurement value in a current sensor and comparing the value with an actual DC voltage measurement value is known (for example, refer to PTL 1). However, in this method, it is difficult, to determine which part of the high DC voltage detection circuit fails, and it is difficult to let a failure part perform a backup operation appropriately.